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BACKGROUND

Apixaban and rivaroxaban are oral direct factor Xa inhibitors, primarily eliminated through CYP3A4-mediated metabolism and direct intestinal excretion. Previous studies suggest that palbociclib, a CDK4/6 inhibitor, may increase the systemic exposure of these anticoagulants; however, the specific pharmacokinetic mechanisms remain unclear. This study aims to evaluate the effects of palbociclib on the pharmacokinetics of apixaban and rivaroxaban using a rat model to optimize combined drug regimens.

METHODS

Male Sprague-Dawley rats were divided into eleven groups to assess interactions between palbociclib and either apixaban or rivaroxaban (n=6). Rats received single or combined doses of palbociclib (11 mg/kg), apixaban (0.25 or 0.5 mg/kg), or rivaroxaban (1 or 2 mg/kg), administered either simultaneously or with a 12-hour interval. Plasma drug concentrations were measured at multiple time points using UPLC-MS/MS, and pharmacokinetic parameters (AUC, Cmax, CLz/F, and Vz/F) were calculated. Additionally, mRNA expression levels of CYP3A4, P-glycoprotein and BCRP in liver and intestinal tissues were analyzed via qRT-PCR to elucidate the underlying interaction mechanisms.

RESULTS

The results demonstrated that palbociclib significantly increased the exposure of both apixaban and rivaroxaban. Specifically, palbociclib elevated the AUC and Cmax of apixaban by approximately two-fold (2.06-fold, p = 0.006 and 2.09-fold, p = 0.006) and rivaroxaban by nearly four-fold (3.81-fold, p = 0.001 and 3.75-fold, p = 0.001), while reducing their clearance and volume of distribution. Even at reduced doses, the exposure to apixaban and rivaroxaban remained disproportionately increased when co-administered with palbociclib. Conversely, administering apixaban or rivaroxaban 12 hours after palbociclib resulted in no significant pharmacokinetic changes.

CONCLUSION

The remarkable increased exposure of DOAC suggest that palbociclib likely enhance intestinal absorption mediated by decreased P-gp and BCRP expression, indicating markedly improved bioavailability for both drugs. These pharmacokinetic interactions provide valuable insights for optimizing dosing regimens of palbociclib in combination with apixaban or rivaroxaban, potentially reducing toxicity risks and enhancing the safety of co-administration in clinical settings.